Abstract
Growth hormone (GH) transgenes can significantly accelerate growth rates in fish and cause associated alterations to their physiology and behaviour. Concern exists regarding potential environmental risks of GH transgenic fish, should they enter natural ecosystems. In particular, whether they can reproduce and generate viable offspring under natural conditions is poorly understood. In previous studies, GH transgenic salmon grown under contained culture conditions had lower spawning behaviour and reproductive success relative to wild-type fish reared in nature. However, wild-type salmon cultured in equal conditions also had limited reproductive success. As such, whether decreased reproductive success of GH transgenic salmon is due to the action of the transgene or to secondary effects of culture (or a combination) has not been fully ascertained. Hence, salmon were reared in large (350,000 L), semi-natural, seawater tanks (termed mesocosms) designed to minimize effects of standard laboratory culture conditions, and the reproductive success of wild-type and GH transgenic coho salmon from mesocosms were compared with that of wild-type fish from nature. Mesocosm rearing partially restored spawning behaviour and success of wild-type fish relative to culture rearing, but remained lower overall than those reared in nature. GH transgenic salmon reared in the mesocosm had similar spawning behaviour and success as wild-type fish reared in the mesocosm when in full competition and without competition, but had lower success in male-only competition experiments. There was evidence of genotype×environmental interactions on spawning success, so that spawning success of transgenic fish, should they escape to natural systems in early life, cannot be predicted with low uncertainty. Under the present conditions, we found no evidence to support enhanced mating capabilities of GH transgenic coho salmon compared to wild-type salmon. However, it is clear that GH transgenic salmon are capable of successful spawning, and can reproduce with wild-type fish from natural systems.
Highlights
Increasing growth rates of fish is one of the primary goals for advancement of aquaculture production
Three main groups of fish were examined: growth hormone (GH) transgenic fish raised in the mesocosm from smolt, wild-type fish raised in the mesocosm from smolt (NT Mesocosm fish), and wild-type fish raised in nature from smolt (NT Nature fish)
Mesocosm rearing from smolt to adulthood only partially restored spawning success to wild-type coho salmon, but critically did increase their reproductive capabilities to a level where relative comparisons to GH transgenic salmon can be made
Summary
Increasing growth rates of fish is one of the primary goals for advancement of aquaculture production. Atlantic salmon containing a chinook salmon growth hormone gene fused to an ocean pout antifreeze promoter is currently under consideration by the United States of America’s Food and Drug Administration for potential approval for human consumption [8]. If approved, it would become the first commercial transgenic animal used for human consumption. Combinations of positive and negative pleiotropic effects (e.g. a mating advantage coupled with reduced viability) could theoretically cause population extinctions [11,21], genetic background of wild-type fish may provide counter-selection to restore population-level fitness [20]. Understanding the ability of GH transgenic strains to reproduce is one critical component of estimating overall net effects on their fitness [22]
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